There are various types of valve connection used to install valves, and each connection type has its own pros and cons. Today, let’s talk about some basic end connection types of valves including welded connections, threaded connections and flanged connections.
1. Socket Weld Connections
The valve simply has a socket with an inner diameter that is ever so slightly larger than the pipe’s outer diameter. The pipe is inserted into the socket, and is welded around the rim. Socket weld connections are usually reserved for smaller sizes, typically 2″ and below. They are permanent connections that are reliably leak-free. This example includes “heat sink” fins which help dissipate heat to protect the seals during welding. Valves with this feature are often referred to as “weld-in-place.”
Socket Weld Ball Valve
Note: These welds should be performed by a trained .professional.Care must be taken to avoid damaging the seats and seals with excessive heat.
The valve end and the pipe end are of equal diameters. The outer edge of each is chamfered to create a “valley” to be filled with welding material. The two pieces are welded around the rims as shown in the illustration. Butt weld connections are usually reserved for smaller sizes, typically 2″ and below.
Butt Weld Ball Valve
Note: These welds should be performed by a trained profesional. Care must be taken to avoid damaging the seats and seals with excessive heat.
3. Threaded Connections
Threaded Ball Valve
Threaded connections are very common. They provide a compact and streamlined connection between the valve and pipe.
The valve typically has female threaded end connections, into which the male threaded pipe fits. There are valves with male threaded connections as well, and even valves with one female end and one male end. Threaded connections must adhere to a standard in order to be useful in industry. There are a few different standards that exist. The valve and pipe must both be created using the same standard in order for them to make a proper connection.
There are standards for straight threads and some for tapered. Tapered threads provide a fluid tight seal without the use of a soft seal like an o-ring or flat washer. Straight threads do require a soft seal that gets compressed between the valve and pipe, hose, or fitting that they are being connected to.
According to the flanged ends either formed together or separately with the valve body, there are three flanged connection types of valves: Raised Face(RF), Ring Type Joint(RTJ) and Flat Face(FF).
(1) The Raised Face flange is the most common type used in process plant applications, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face. This face type allows the use of a wide combination of gasket designs, including flat ring sheet types and metallic composites such as spiral wound and double jacketed types.
(2) The Ring Type Joint flanges are typically used in high pressure (Class 600 and higher rating) and/or high temperature services above 800°F (427°C). They have grooves cut into their faces which steel ring gaskets. The flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or Coining) the gasket to make intimate contact inside the grooves, creating a metal to metal seal.
(3)The Flat Face flange has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.
The mating surface of the flanged valve connection is called the face. The face is usually machined to create a smooth surface which will help assure a leak-proof seal when two flanges are bolted together with a gasket sandwiched between.